Census 2021: How do official population figures compare to estimates?

A Census 2021 envelope ahead of all households being asked to complete the census ahead of Census Day on Sunday. Picture date: Saturday March 20, 2021.

We now have more robust figures on the size and characteristics of Arun’s population.

But how do they compare to estimates which are used by decision makers in central and local government to understand their communities’ needs?

Mid-year population estimates are produced annually by the Office for National Statistics and are based on the most recent census.

The ONS rolls forward information from registers for births, deaths and migration surveys to produce each year’s estimate – but it means the further away from the census, the more uncertain they are.

ONS statisticians estimated there were 161,123 people of all ages living in Arun as of mid-2020 – below the 2021 census figure of 164,800.

Snapshot data from the census in March 2021 tells us there were 46,900 (28.5%) over-65s living in the area, compared to the 46,898 (29.1%) estimated by the ONS.

There are more males in Arun than estimated by the ONS – 2021 census results revealed 79,400 males (48.2%) were usual residents, while the mid-2020 prediction was 77,506 (48.1%).

The latest estimates suggested there were 83,617 (51.9%) females in the area, and on census day, 85,400 (51.8%) said Arun was their home.

The ONS says population statistics are “vital in making a range of decisions and informing public debate".

During the coronavirus pandemic, estimates have been used to measure vaccine uptake at a national and regional level, while they are also used to measure unemployment rates, forecast pensions and make decisions about local services – such as the number of school places of the provision of health services for an ageing population.

The 2020 mid-year population estimate for England and Wales as a whole stood at 59.7 million – very close to the 2021 census figure of 59.6 million.

The ONS noted that population change in certain areas "may reflect how the coronavirus pandemic affected people’s choice of usual residence on census day".

“These changes might have been temporary for some and more long-lasting for others," it added.